Avoidance of allergens remains a cornerstone in the management of patients with allergic diseases. However, many allergens, such as those associated with dust mites, other insects, and animal danders, are ubiquitous in the environment and cannot be entirely avoided. Therefore, effective avoidance measures should be tailored to the specific allergens that are important for a particular patient. The clinician should also focus on environments that can be altered (ie, indoor spaces) and those in which the patient spends significant time. In this context, allergen sampling of the environment may be clinically useful.

This topic will discuss the identification of allergens, indications for allergen sampling, and methods for sampling and measuring allergens, with a focus on aeroallergens in the indoor environment. Indicators of quality testing methods that the clinician can use to identify an appropriate testing laboratory are also discussed. Testing of individuals to determine sensitivity to specific allergens and measures to reduce indoor allergen exposure are presented elsewhere. (See "Overview of skin testing for allergic disease" and "Allergen avoidance in the treatment of asthma and allergic rhinitis".)

IDENTIFICATION OF ALLERGENS

An allergen is a natural substance that is generally innocuous to most people, but when introduced into a genetically-predisposed individual, elicits the formation of immunoglobulin E (IgE) antibodies specific to that substance. These allergen-specific IgE antibodies bind to IgE receptors on the surface of the individual's mast cells and basophils. When the subject is re-exposed to that allergen, the allergen binds multiple IgE molecules in the cells' surface, generating activation signals. Mast cell and basophil activation results in the release of an array of inflammatory mediators that precipitate the symptoms of allergic disease.

The identification of clinically-important allergens in an environment begins by obtaining clinical histories from affected individuals who, when exposed to a given substance, develop similar signs and symptoms that are known to represent IgE-mediated allergic disease. This process is undertaken when new allergens are suspected in a population. In the past few decades, several new allergens have been identified, such as Asian ladybugs and stink bugs, and new occupational allergens are regularly identified among manufacturing workers.

Making the connection between symptoms and a specific exposure is most straightforward when allergic symptoms appear shortly after exposure (eg, anaphylaxis following ingestion of peanuts, severe rhinitis or asthma following grass cutting). In contrast, allergens to which people are chronically exposed are much more difficult to identify. As an example, it took several decades to identify the dust mite as the primary source of allergenic material in house dust [1]. In addition, allergen dose and route of exposure also affect the clinical presentation [2]. Allergens that are inhaled or injected usually cause more immediate symptoms compared with those that are ingested.

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